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Introduction
Traditional terrestrial
landline Telstra payphones are not intelligent in their own
right and thus require a Called Subscriber Answer (CSA)
signal, sent from the telephone exchange, in order for the
payphone to collect the cost of the call. Alternate
Technologies include on-board rate-table databases which
dynamically calculate the required cost of a call based on a
set of rules relating to what area code or country code the
dialled number belongs to.
CALLED SUBSCRIBER
ANSWER (CSA)
When the called party
answers on a chargeable call, the telephone exchange sends a
two-part signal to the payphone, made up of a line reversal (LR)
and a meter pulse (MP). This two-part signal is termed Called
Subscriber Answer (CSA). The line reversal indicates the call
is chargeable and the meter pulse, be it 50 Hz or 12 kHz, will
cause the payphone to collect the cost of the call. The
sending sequence of CSA is important, it is always a line
reversal followed by a meter pulse. Should the sequence be
reversed, occur simultaneously or one part be missing, then
the payphone may not operate correctly
METER PULSE
After the exchange has
sent a “line reversal” it waits a finite time before
sending the meter pulse - this is generally termed "Start
Delay" The approximate start delay for AXE is 1 second
+/- 50 ms, for System 12 (S12) it is 300 ms +/- 50- ms. The
Goldphone, Bluephone, HandiPhone (DTOP) andTelstra Smartphone
will accept a meter pulse, be they either 50 Hz or 12 kHz
(depending on the model) starting 50 ms after line reversal.
Characteristics The meter
pulse sent by the exchange has three characteristics namely
– frequency, duration (how long for) and level (how much
voltage).
A 50 Hz meter pulse,
because of the way it is sent and its higher level can be
detected by a payphone over a longer cable pair than a 12 kHz
meter pulse.
Click
to access circuit diagrams and description of CLM 12 khz
(applies to Diamond Bluephones, and
Telstra smartphones)
Click
to access circuit diagrams and description of CLM 50 khz
(applies to old-style payphones like the Telecom
Goldphone)
Click
to access circuit diagrams and description of the network
exchange CSA setup used in typical Telstra
systems.
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